This application claims the benefit of and priority from Japanese Applications No. 2000-169913 filed Jun. 7, 2000 and No. 2001-98077 filed Mar. 30, 2001, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a tank cap to close a tank opening member and a tank cap apparatus with the tank cap attached thereto.
2. Description of Related Art
In conventional practice, tank caps are configured such that a fuel supply port is closed by rotating a fuel cap fitted with a gasket several times relative to a filler neck connected to a fuel tank. Since rotating the fuel cap a plurality of times sometimes fails to result in a tight fit, closing the fuel supply port of a filler neck with a fuel cap merely by turning the cap through a predetermined angle (for example, about 90xc2x0) has been proposed as a way of overcoming this shortcoming.
FIG. 24 is a diagram depicting the state existing before a fuel cap is mounted over a filler neck. The fuel cap 100 comprises a casing main body 102 for opening and closing the fuel supply inlet FNb of a filler neck FN, a cover 104 mounted on the casing main body 102, and a gasket GS mounted in the upper portion of the casing main body 102. A ratchet mechanism (not shown) is interposed between the casing main body 102 and the cover 104 to ensure that the cover 104 idles relative to the casing main body 102 when excessive torque is applied between the cover 104 and the casing main body 102.
A casing engagement element 102a is also formed in the lower portion of the outer circumference of the casing main body 102. An opening engagement element FNc is further formed in the inner circumferential portion of the filler neck FN. Part of the area around the inside of the opening engagement element FNc is provided with a neck insertion notch FNd for allowing the casing engagement element 102a of the fuel cap 100 to be inserted in the axial direction.
FIG. 25 is a diagram depicting the manner in which the fuel cap 100 is mounted over the filler neck FN. The opening engagement element FNc is tapered by a prescribed inclination xcex1 in the axial direction, and the guide surface 102b of the casing engagement element 102a is tapered to match this angle.
The manner in which the inlet FNb of FN is closed with the fuel cap 100 will now be described. The casing engagement element 102a is positioned in the neck insertion slot FNd, and the fuel cap 100 is turned through a predetermined angle (about 90xc2x0) while the fuel cap 100 is inserted into the filler neck FN. By this, the fuel cap 100 is mounted over the filler neck FN as a result of the fact that the casing engagement element 102a is caused to align with and engage the opening engagement element FNc. At the same time, the gasket GS is compressed between the casing main body 102 and the filler neck FN, forming a seal. If rotated further, the cover 104 will idle due to the presence of the ratchet mechanism, signaling that the limit has been reached and indicating that the fuel cap 100 fits tightly over the inlet FNb.
Reducing the inclination xcex1 of the opening engagement element FNc during the closure of the fuel cap 100 will increase the operating angle of the fuel cap 100, not only making the cap more difficult to operate but also allowing the fuel cap 100 to occasionally rotate through an angle greater than 180xc2x0 and come off. Conversely, increasing the inclination xcex1 will increase the tightening rate of the gasket GS (that is, the extent to which the gasket GS is compressed) and will enhance the rubber recoil of the gasket GS. For this reason, the rotational torque will increase and the cover will be idled by the ratchet mechanism before the gasket GS is adequately compressed, making it impossible to form a tight seal.
This approach is thus disadvantageous in the sense that it is difficult to cause the gasket GS to form a tight seal by rotating the fuel cap 100 through a narrow operating angle (about 90xc2x0). In addition, considerable load is applied between the opening engagement element FNc and the corner 102c of the casing engagement element 102a when the corner 102c is pressed against the opening engagement element FNc. A greater rotational torque is therefore needed to close the fuel cap 100, sometimes making it impossible to close the cover properly and form a tight seal.
One aspect of the present invention provides a tank cap apparatus in which a seal member can form a better seal with a small operating angle.
In accordance with one embodiment of the present invention, a tank cap apparatus comprises a tank opening member having an opening engagement element and a cap constructed and arranged to close the tank opening member through rotation. The cap includes a cap engagement element for engaging the opening engagement element and a gasket interposed between the cap and a sealing surface of the tank opening member and constructed and arranged to seal the gap therebetween. The opening engagement element is inclined at a predetermined angle relative to a direction orthogonal to an axial direction for closing the cap and the cap engagement element has a guide surface for engaging the opening engagement element by a rotation of the cap in a closing direction while the cap is inserted into the tank opening member. An angle of the guide surface decreases with a rotation of the cap in the closing direction.
In the tank cap apparatus according to the present invention, inserting the cap into the tank opening member and rotating the cap in the closing direction will seal the gap between the cap and the tank opening member. This is because a cap engagement element will engage and fit over an opening engagement element, and the seal member interposed between the cap and the tank opening member will be compressed.
During cap closure, the guide surface of the cap engagement element aligns with and engages the opening engagement element. The guide surface is configured such that the angle thereof diminishes as the cap is rotated in the closing direction during this process. Specifically, the configuration is selected such that the inclination is greater in the initial stage. Despite the fact that the inclination of the guide surface is thus increased in the initial stage and the tightening rate is kept at a higher level, the torque is prevented from becoming excessively high and the seal member can be provided with an adequate tightening margin because the seal member produces only a weak reaction force during the initial compression stage of the seal member. When the seal member is compressed past the initial stage, the guide surface acquires a lesser angle and becomes capable of consistently providing a better seal in a state in which the tightening rate of the seal member is reduced.
Accordingly, aligning the steeply inclined guide surface with the opening engagement element during the initial compression stage of the seal member makes it possible to provide the seal member with an adequate tightening margin (and hence to obtain a tight seal) without creating a strong reaction force even in the case of a narrow rotation angle.
As a preferred embodiment of such a guide surface, a simple structure can be formed by providing a first inclined portion configured at an inclination whose angle with respect to the direction orthogonal to the axial direction is greater than the angle of the opening engagement element, and providing a second inclined portion formed as a continuation of the first inclined portion and inclined at an angle substantially equal to the aforementioned predetermined angle. The cap engagement element can be easily formed with high precision by being injection-molded monolithically with the casing main body despite being configured with a slightly varying incline in order to obtain the first and second inclined portions. In addition to the configuration in which the second inclined portion is formed as a surface that continues past the first inclined portion, it is also possible to adopt a configuration in which a third inclined portion is provided at an inclination that is intermediate between those of the first and second inclined portions.
According to another embodiment of the guide surface, it is possible to provide a structure in which the angle of inclination relative to the direction orthogonal to the axial direction is greater than the predetermined angle of the opening engagement element. In addition to being fashioned as a planar surface of constant inclination, the guide surface may also be fashioned as a curved surface or configured in accordance with a variety of other possible embodiments in which a continuously varying inclination is adopted.
Preferred embodiments of the seal member include C-rings, O-rings, and various other types of seal members characterized by exerting weak reaction force when compressed in the initial stage.
In accordance with another embodiment of the preset invention, a tank cap for closing a tank opening member provided with an opening engagement element formed in an inclined state at a predetermined angle comprises a casing main body including a flange formed in an upper portion of the casing main body, a gasket holder disposed underneath the flange, and a cap engagement element formed underneath the gasket holder. The gasket is held by the gasket holder and seals a gap around a sealing surface of the tank opening member. The cap also includes a cover rotatably mounted over the flange. The cap engagement element has a guide surface for engaging the opening engagement element by a rotation of the cap in a closing direction while the cap is inserted into the tank opening member. An angle of the guide surface decreases with a rotation of the cap in the closing direction.
In the tank cap apparatus according to the present invention, inserting the cap into the tank opening member and rotating the cap through an angle 180xc2x0 or less in the closing direction will cause a cap engagement element to engage and fit into an opening engagement element and to seal the gap between the cap and the tank opening member by compressing the gasket interposed between the cap and the sealing surface of the tank opening member.
As the cap engagement element projects from the outer circumference of the cap, a gap is left between the outer circumferential surface of the cap and the inner wall of the tank opening member in the area not covered by the cap engagement element, but this gap is filled with a tilt-preventing rib. An outside cap-tilting force pushes the tilt-preventing rib against the inner wall of the tank opening member, allowing the cap to tilt only slightly. Accordingly, the gasket retains its sealing properties without undergoing excessive plastic deformation.
It is also possible to adopt a structure in which the tilt-preventing rib is disposed above the area not covered by the cap engagement element. Furthermore, the arrangement in which the tilt-preventing rib is formed around the entire cap periphery can be abandoned in favor of an arrangement in which the rib is provided in divided form at locations that are best suited for the prevention of cap tilting. In addition, extending the tilt-preventing rib to a height substantially equal to or greater than the radial height of the cap engagement element causes the rib to come into contact with the inner wall of the tank opening member and to prevent the cap from tilting and the cap engagement element from coming into contact with the inner wall of the tank opening member when a cap-tilting force is applied.
According to another embodiment of the invention, there is provided a tank cap for closing a tank opening member by rotating the cap through an angle of 180xc2x0 or less to bring the cap into engagement with an opening engagement element formed on the inner wall of the tank opening member, wherein this cap comprises a casing main body comprising a flange formed in the upper portion thereof, a gasket holder disposed underneath the flange, and a cap engagement element fashioned as a projection underneath the gasket holder. The cap also comprises a gasket held by the gasket holder and designed to seal the gap around the sealing surface of the tank opening member and a cover rotatably mounted over the flange. The casing main body further comprises a tilt-preventing rib formed as a projection on the outer circumferential portion of the casing main body above the cap engagement element but below the gasket, and designed to come into contact with the inner wall of the tank opening member and to prevent the casing main body from tilting upon application of a force that tends to tilt the casing main body.
In addition to the means whereby the cap and the opening engagement elements are engaged merely by being rotated through an angle of 180xc2x0 or less, a torque mechanism for achieving an engagement through a prescribed rotational torque can be provided as a means whereby the cap engagement element is brought into engagement with the opening engagement element by rotating the tank cap through an angle of 180xc2x0 or less.
These and other objects, features, aspects, and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with the accompanying drawings.